The present invention relates to a joist for building constructions, comprising an elongated, form-stable body with a flat outer side and an inner side. The body is provided with a plurality of circular through-holes spaced from each other and extending perpendicularly to and between the outer and inner sides. The walls of the holes are provided with threads with predetermined pitch, and a plurality of load-bearing space and level adjusters of straight, circular cylindrical shape. Each space and level adjuster has an external thread of the same pitch as the thread of the hole wall and is provided with engagement structure accessible from the outside of the joist body for co-operation with a turning device. The space and level adjusters have a diameter of 10-40 mm, preferably 15-25 mm, and are screwed into the holes with their front portions protruding from the joist body to form an air gap between the supporting surface and the joist body and to adjust the outer side of the joist body at a desired level. The remaining portion of the space and level adjuster is in firm thread engagement with the joist body, and the rear end is located below or in plane with the outer side of the joist body.
When building a floor construction, for instance, solid floor joists are used that usually consist of timber and due to their sealing effect, the air circulation under the finished floor is poor, or even non-existent. This often contributes to problems of damp and mold occurring. Furthermore, the floor joist is generally in direct contact with the supporting surface, and if this is damp, the floor joist may absorb this dampness and the moisture-absorbing parts gradually rot. Expensive clearance work and reconstruction are then required when the resultant unavoidable damage is to be repaired. The level of the floor is also determined by the dimension of the floor joists, and the range of floor joists can therefore be relatively large if all requirements for different floor levels are to be satisfied. Unevenness of the supporting surface is another difficulty with regard to installing the joists at the correct level.
The object of the present invention is to greatly reduce the problems mentioned above and provide a joist that will enable air to circulate as well as being easy to install at the desired level, and which can be easily and quickly produced even directly on site where the joists are to be used.
The joist according to the present invention is substantially characterized in that the threads in the holes are effected directly in the joist body, that said threads on the space and level adjusters extend from end to end, that the space and level adjusters have a length such that a rear portion situated inside the joist body in order to maintain the requisite thread engagement, has a part-length of at least 10 mm, preferably at least 20 mm, whereas the front portion has a part-length of at least 1 mm, preferably at least 5 mm, in order to form the air gap, and that the space and level adjusters are arranged in the central plane of the joist body, bisecting the outer and inner sides at right angles and/or in two rows and alternating on each side of the central plane of the joist body.